1. Field of the Invention
The invention covered by the present patent application relates to a method for the production of an electron source substrate provided with an electron emitting element and a method for the production of an electronic device using the substrate.
2. Related Background Art
The electron emitting element has been heretofore known in two broadly divided types, i.e. the thermoelectron emitting element and the cold cathode electron emitting element. The cold cathode electron emitting element comes in such types as the field emission type (hereinafter referred to as xe2x80x9cFE typexe2x80x9d), metal/insulating layer/metal type (hereinafter referred to as xe2x80x9cMIM typexe2x80x9d), and surface conduction type, for example.
As examples of the FE type electron emitting element, those elements which are disclosed in W. P. Dyke and W. W. Doran, xe2x80x9cField Emission,xe2x80x9d Advance in Electron Physics, 8, 89 (1956) or C. A. Spindt, xe2x80x9cPhysical Properties of Thin-film Field Emission Cathodes with Molybdenium Cones,xe2x80x9d J. Appl. Phys., 47, 5248 (1976) have been known.
As an example of the MIM type electron emitting element, the element which is disclosed in C. A. Mead, xe2x80x9cOperation of Tunnel-Emission Devices,xe2x80x9d J. Appl. Phys., 32, 646 (1961) has been known.
As an example of the surface conduction type electron emitting element, the element which is disclosed in M. I. Elinson, Radio Eng. Electron Phys., 10, 1290 (1965) has been known.
The surface conduction type electron emitting element utilizes a phenomenon that flow of an electric current parallel to the surface of a thin film of small area formed on a substrate results in emission of electrons. The surface conduction type electron emitting elements include the element using a thin film of Au reported in G. Dittmer: Thin Solid Films, 9, 317 (1972), the element using a thin film of In2O3/SnO2 reported in M. Hartwell and C. G. Fonstad: IEEE Trans. ED Conf., 519 (1975), and the element using a thin film of carbon reported in Hisashi Araki et al.: Vacuum, Vol. 26, No. 1, page 22 (1983) in addition to the element using a thin film of SnO2 proposed by Elinson as mentioned above.
As a typical example of the surface conduction type electron emitting element, the construction of the element proposed by M. Hartwell et al. as mentioned above is illustrated in the form of a model in FIG. 20. In the figure, 1 denotes a substrate and 4 an electroconductive thin film which is formed of a metal oxide in the pattern shaped like the letter H by sputtering and so forth and made to incorporate therein an electron emitting portion 5 by a treatment of electrification called an energization forming which will be specifically described herein below. As illustrated in the figure, the interval L between element electrodes 2 and 3 is set at a length in the range of 0.5 to 1 mm and the width W"" of the thin film at 0.1 mm. The electron emitting portion 5 is illustrated by way of model because the position and shape thereof are unclear or indefinite.
In the surface conduction type electron emitting element of this class, the practice of subjecting the electroconductive thin film 4 to the treatment of electrification called energization forming in advance of the emission of electrons thereby forming the electron emitting part 5 thereof has been in vogue. To be specific, the energization forming is aimed at causing an electron emitting portion to form by means of electrification. It consists, for example, in applying a DC voltage or very gradual elevation of voltage to the opposite terminals of the electroconductive thin film 4 mentioned above thereby forcing this thin film to sustain local fracture, deformation, or degeneration and, as a result, allowing formation of the electron emitting portion 5 in an electrically highly resistant state. The treatment, for example, locally inflicts a fisure to the electroconductive thin film 4 to enable this thin film to emit electrons from the neighborhood of the fisure. The surface conduction type electron emitting element which has undergone the energization forming treatment mentioned above is such that it is enabled to effect emission of electrons from the electron emitting part 6 in response to the application of voltage to the electroconductive thin film 4 and the consequent induction of flow of an electric current through the element.
The surface conduction type electron emitting element of the quality described above enjoys simplicity of construction and allows for the manufacture thereof by the use of the conventional technique of semiconductor production and, therefore, brings about the advantage of enabling a multiplicity of surface conduction type electron emitting elements to be formed as arrayed over a large surface area. Various applied studies in the application of this characteristic feature have been conducted. Charged beam sources and image forming devices such as display apparatuses may be cited as apt examples of the targets of the applied studies.
The construction of the electron emitting element disclosed by the present applicant for patent in JP-A-02-56822 is illustrated in FIG. 19. In this diagram, 1 denotes a substrate, 2 and 3 each an element electrode, 4 an electroconductive thin film, and 5 an electron emitting portion. Various methods are available for the production of the electron emitting element. For example, the electron electrodes 2 and 3 are formed on the substrate 1 by the vacuum thin-film technique popular in semiconductor processes and the photolithographic etching technique. Then, the electroconductive thin film 4 is formed by a dispersion coating method such as, for example, the spin coat. Thereafter, the electron emitting part 5 is formed by applying voltage to the element electrodes 2 and 3 thereby effecting a energization treatment. The conventional method-of production cited above, when used to form a multiplicity of elements arrayed on a large surface area, has the disadvantage of rendering indispensable the provision of a photolithographic etching device of large scale, necessitating a large number of steps, and exalting the cost of production. As a means for overcoming these defects by patterning the electroconductive thin film of the surface conduction type electron emitting element without using the semiconductor process, a method for directly depositing a solution containing a metallic element in the form of liquids on a surface by the principle of ink jet has been proposed (as in JP-A-08-171850).
The conventional ink jet methods which are disclosed in JP-A-08-171850 and so forth, however, effect the direct deposition of liquids by the use of such a single head as is illustrated in FIGS. 18A, 18B, and 18C (the component parts illustrated therein have the same meanings as those of FIG. 19). As the substrate gets larger in surface area, a lot of time is required for patterning one substrate, and there is a limit on the increase in the throughput. The conventional methods also have the disadvantage of boosting the cost of equipment because it requires the stroke of the relative motion between the substrate and the head to be increased in accordance with the size of the substrate.
The task assigned to the present invention consists in decreasing the time required for the production of the electron source substrate, increasing the yield of the production of electron source substrates, and improving the electron source substrate in quality.
One of the objects of the present invention is to shorten the time for production of an electron source substrate. For this object, the present invention is constituted as below.
The process of the present invention produces an electron source substrate having plural electron-emitting elements having respectively a pair of element electrodes counterposed with a spacing, an electroconductive film placed in the spacing and connected to both of the pair of element electrodes, and an electron-emitting portion formed in the electroconductive film. The process comprises a step of forming the electroconductive films by application of a metal element-containing solution in a state of a liquid onto regions of the electroconductive film formation on the substrate, wherein at least one liquid outlet is counterposed to each of the regions having respectively plural sites for electroconductive film formation, and the liquid outlets and the substrate are moved relatively to apply the liquid at least once onto the respective sites for electroconductive film formation.
The time for the production can be reduced, and the relative movement range can be reduced by application of the liquid from the outlets to the respective regions.
The range of the relative movement of the liquid outlets and the substrate can be decreased by fixing the relative positions of the plural liquid outlets. The relative positions of the plural outlets are preferably adjusted preliminarily.
In the present invention, the aforementioned plural regions are formed by dividing the area for the electroconductive film formation on the substrate in a first direction and a second direction not parallel to the first direction. The liquid can be applied onto the respective regions by discharge of the liquid from the liquid outlet, with movement (scanning) of the liquid outlets in the first direction, onto the respective sites of the electroconductive film formation, displacement of the liquid outlets in the second direction, and successive discharge of the liquid thereon with movement in the first direction.
The liquid application can be conducted efficiently by making the plural regions in a congruent shape in the present invention.
At least one head may be provided for each of the plural regions, and at least one liquid may be provided in each head in the present invention.
In the case where the liquid is applied in plural times in one electroconductive formation site, the process of the present invention is constituted as below for preventing deformation of the electroconductive film or for improving the uniformity of the electroconductive film.
The process of the present invention produces an electron source substrate having an electron-emitting element comprising a pair of element electrodes counterposed with a spacing, an electroconductive film placed in the spacing and connected to both of the pair of element electrodes, and an electron-emitting portion formed in the electroconductive film. The process comprises a step of forming the electroconductive film by application of a metal element-containing solution in a state of a liquid from the liquid outlet two or more times onto the portion of the electroconductive film region on the substrate, wherein the time interval between one liquid application and the succeeding liquid application is larger than the time length for controlling the spreading of the succeedingly applied liquid within an allowable limit.
In this configuration of the invention, in applying a liquid onto plural electroconductive film formation sites, the number of the electroconductive film formation sites, the temperature or humidity in the liquid application, the solution composition of the applied liquid, the solvent composition of the solution, and so forth are suitably selected to satisfy the above conditions in the second or later application of the liquid and to shorten the waiting time.
In the case, in the present invention, where at least one liquid outlet is counterposed to respective plural regions having respectively plural sites for electroconductive film formation, and the liquid outlet and the substrate are moved relatively to apply the liquid at least once onto the respective sites for electroconductive film formation, the conditions of the temperature or humidity in the liquid application, the solution composition of the applied liquid, the solvent composition of the solution, and the number of the divided subregions of the electroconductive film area are suitably selected to satisfy the above conditions of the time interval of the application of the liquid and to shorten the waiting time.
The aforementioned time interval for suppressing the spreading of the succeedingly applied liquid within an allowable limit herein may be a time interval to retain the spreading of the succeedingly or later applied liquid within the approximate range of spreading of the firstly applied liquid, or may be a time interval for suppressing the spreading of the liquids in each liquid application to attain finally acceptable spreading range for preparation of a desired electron-emitting element when the liquid is applied two or more times. More specifically, the time interval may be longer than 1.8 seconds.
In the present invention, the liquid application may be conducted by an ink-jet system. Specifically, the ink-jet system may be the one employing thermal energy to generate bubbles in a solution to eject the solution by the bubbles, or may be the one employing a piezo-element to eject the solution.
The process of the present invention for producing an electronic apparatus having an electron source substrate having plural electron-emitting elements comprises a pair of element electrodes counterposed with a spacing, an electroconductive film placed in the spacing and connected to both of the pair of element electrodes, and an electron-emitting portion formed in the electroconductive film; and an irradiation-receiving member to be irradiated by electrons emitted from the electron-emitting element: the process comprising producing the electron source substrate produced by any of the above methods for producing the electron source substrate.
The irradiation-receiving member may be an image-forming member which forms an image by irradiation of electrons, a light emitter or a phosphor which emits light by irradiation of electrons.